Several documents report epoxidation process with hydrogen peroxide by using as catalyst, heteropolyacid prepared separately and a quaternary ammonium salt being a phase transfer catalyst (see, for example, J. Org. Chem., Vol. 53, p. 1553-1557 (1988) and J. Org. Chem., Vol. 53, p. 3587-3595 (1988)). The epoxidation process yields only water other than the product and therefore is a very clean oxidation reaction.
However, the above-mentioned process is not necessarily a satisfactory industrial production process from reason that it uses solvents such as chloroform, dichloromethane, benzene or the like that are not used in ordinary industrial production processes, and the like. In addition, in the above-mentioned documents, although oxidation catalysts are prepared by using alkyl ammonium salt such as methyltrioctyl ammonium chloride, the oxidation catalysts have a high partition coefficient for organic solvents, and it is difficult to separate with products dissolved in organic solvents. Therefore, the process has problems in the separation and re-use of oxidation catalyst.
On the other hand, is also reported a process for making an oxidation catalyst heterogeneous by using an inorganic compound such as silica gel as a carrier (see, for example, JP 2001-17863A and JP 2001-17864 A). This process requires an expensive silane coupling agent or the like as an auxiliary substance for heterogenization, and therefore is not necessarily a satisfactory process. Industrially, further preferable oxidation catalysts are desired.
Therefore, an object of the present invention is to provide a process for producing oxirane compounds which is clean and industrially useful, and an olefin oxidation catalyst which is excellent in separability from a reaction solution and re-usability.